(a) Field
The subject matter disclosed generally relates to distributed pyrolysis of waste using microwaves as a source of heating.
(b) Related Prior Art
Conventional commercial pyrolysis systems use a fuel-based source of heating where heat is transferred from the wall surface by convection, radiation and conduction to the material. This approach generally leads to an autothermal process where the gas generated by the pyrolysis reaction is used to heat the material.
To date, the pyrolysis of municipal and/or domestic waste using microwave has not been of interest for the following reasons. 1) Typically, these wastes exhibit low thermal response in a microwave field at low powers. At high enough microwave power, virtually any material would heat in microwaves. However, the power required may be substantial. 2) Unassisted/non-catalytic microwave processing of microwave-transparent materials requires a net input of energy, such as electricity, to trigger the pyrolysis reaction which results in a huge energy consumption for large scale pyrolysis processes as opposed to the fuel based heating source approach which supplies its own energy by means of the reaction itself. 3) Municipal and/or domestic waste contains a relatively high amount of water which makes the pyrolysis process generally endothermic due to the large amount of water that evaporates in the early stages of the reaction. Conventional pyrolysis of high-moisture materials requires a substantial energy input for water removal and breakdown of organics. Unassisted low-power microwave processing of high-moisture microwave-transparent feedstocks leads only to drying as opposed to pyrolysis.
U.S. Pat. No. 6,139,744 deals with conventional pyrolysis of human and animal waste in liquid phase using a combustion chamber using heating elements and microwaves. The system separates the solids from the liquids and performs combustion of the solid waste using the magnetron of a microwave device and a heating element. There is also disclosed a microbial treatment of the liquid stream. The microwave heating is not assisted and it is not the only source of heating as heating elements are used to start the combustion process.
U.S. Pat. No. 5,387,321 deals with the pyrolysis of microwave-transparent waste using a microwave absorbing bed of carbonaceous material. However, the process is employed to pyrolyse a continuous flow of microwave-transparent waste, such that oxygen may enter with the incoming waste stream, and therefore requires means of controlling the atmosphere in the reaction chamber such that flame generation (combustion) is substantially prevented therein.
The present invention will reduce the volume of waste at the source by at least 90%, which will reduce transportation, collection and disposal costs of waste that represent from about 60% to about 70% of the total expenditures related to current waste management strategies. Also, the present invention also results in the production of energetic by-products that may be sold and used or even reused on site. The process and system are used locally, at the source of production of the waste, and the by-products may be collected and reused at the source or outside the source, effectively resulting in a distributed pyrolysis operation as opposed to a centralized operation.
There remains a need to introduce pyrolysis into small to medium-scale at source processing of waste for inertization and volume minimization, with the added value of generating useful and/or saleable products. A preferred way to carry out small to medium-scale waste pyrolysis would be microwave heating because it leads to a compact controllable low-risk system to the user.